The present invention relates to a bifunctional environment sensor, and in particular to such a bifunctional environment sensor which can detect the values of two different physical quantities at the same time.
Conventionally, for sensing the values of various parameters of the external environment such as temperature, humidity, gas concentration, smog concentration, smoke concentration, and so on, methods are known for making use of electroconductivity in metal oxides and resins and so on, and methods using semiconductor material and so on are known. Devices utilizing such principles are also known; however, such devices have always only been able to detect the value of one parameter of the external environment, and no device has been proposed which can detect the values of two environmental parameters at the same time, such as the values of any two of temperature, humidity, gas concentration, smog concentration, and smoke concentration. In other words, one sensing device has hitherto been capable only of detecting the value of one physical quantity, and in order to detect the values of two different physical quantities two sensing devices having different properties have had to be used.
However, in the case of many such sensing devices for various parameters, and particularly in the case of humidity sensing devices for sensing relative humidity, sometimes they have temperature dependence, and accordingly it has been practiced to correct or to compensate the humidity value sensed by such a humidity sensing device according to the value of the output of another sensor for sensing the ambient temperature around said humidity sensing device, said temperature sensing device being placed adjacent to the humidity sensing device and as near to it as possible. However, this correction method leads to problems. For instance, if the base boards of the two sensor devices have different thermal conductivities, then the speed of response of the two sensor devices is different, and accurate correction of the humidity readings provided by the humidity detector according to the temperature readings provided by the temperature sensor cannot be performed. Therefore, accurate values of physical quantities cannot be practicably sensed in this way. Further, if two such separate sensor devices are used, then the combination cannot be made compact, and the cost thereof tends to be high.